Conductive polymer thick film (PTF) compositions are becoming increasingly advantageous for use in various electronic components in a number of applications, including, but not limited to, low temperature hybrid systems. LED applications, automotive applications, power electronics, low temperature heater applications, antenna or radio frequency applications, and fuel cells. Commonly, such PTF compositions are used to form conductive layers on various substrates. Because conductive PTF compositions typically do not have a glass component (as do conventional thick film materials used in similar applications), they do not require the high firing temperatures (e.g., above 500° C.) of conventional thick film materials. Many conductive PTF compositions may be processed at temperatures between about 120° C. and 350° C. As such, the use of conductive PTF compositions reduces processing times and thus manufacturing costs associated with the manufacture of electronic circuit devices, furthermore, conductive PTF compositions may be used with a variety of substrates which require lower processing temperatures.
One concern with conductive PTF compositions is that they are difficult to solder to. Many conductive PTF compositions that are solderable use lead-based solders, which are soldered at relatively low temperatures (e.g., between about 200° C. and 270° C.) as compared to lead-free solders (e.g., between about 230° C. and 300° C.). However, lead-free solders are preferred due to environmental concerns. Because of the compositions of conductive PTF materials, their processing temperatures are lower, and thus the use of high-temperature lead-free solders is disadvantageous as leaching of the conductive component (e.g., silver) in the composition material may occur. When leaching occurs, the remaining polymer material is not solderable and leaves an unusable layer.
International Patent Publication No. WO2012/067705 teaches a polymer thick film composition solderable with lead-based solder. There is a need for a conductive PTF composition that may be directly soldered to using lead-free solder. Thus, an object of the invention is to provide a conductive PTF composition for use in low-temperature applications that is able to withstand the higher lead-free soldering temperatures.